The present invention relates to a cutter knife in which the blade is slidably retracted into an elongated sleeve member. In particular, the present invention relates to a cutter knife wherein a space is kept between the blade edge and an inner wall of the sleeve member, in order to prevent the blade edge from being damaged by rubbing against the inner wall of the sleeve member, while sliding.
FIGS. 1 to 3B show a cutter knife, which is disclosed in Japanese examined utility model publication No. 59-20872. A blade 1 and a slider 10 are connected in an elongated sleeve member 20. A user can manipulate the slider 10 to cause the blade 1 to slide, so that the blade 1 is protruded from and retracted into the sleeve member 20. The sleeve member 20 is provided with a pair of side walls 20a and 20b, which extend in parallel to the sliding direction of the blade 1. Being guided between the side walls 20a and 20b, the blade 1 and the slider 10 slide in the longitudinal direction of the cutter knife.
As shown in FIG. 2, a spring member 11 is provided on one side of the slider 10. Under the biasing force by the spring member 11, the blade back 1b is pressed onto the inner surface of the side wall 20a (the side wall at the upper location in FIG. 1). As a result, a space is kept between the blade edge 1a and the inner surface of the side wall 20b (the side wall at the lower location in FIG. 1). Thanks to that space, the blade edge 1a can be prevented from rubbing against the inner surface of the side wall 20b, and thus the blade edge 1a can be protected from damage.
The slider 10 is provided with two engagement protrusions 15, 16, which are located at the forward end and at the rearward end of the slider 10 in the sliding direction. One of the engagement protrusions is inserted into a connection hole 2 of the blade 1, so that the slider 10 and the blade 1 are connected. As shown inside the dash-lined frame in FIG. 1, when the inserting direction of the slider 10 into the sleeve member 20 is reversed, the engagement protrusion 16 is now engaged with the connection hole 2, rather than the engagement protrusion 15. As a result, the direction of the biasing force applied to the blade 1 by the spring member 11 is also reversed. In other words; when the inserting direction of the slider 10 is reversed, and further the blade 1 is turned so that the edge 1a faces upward as shown in FIG. 1, the blade back 1b is pressed onto the inner surface of the side wall 20b under the biasing force of the spring member 11, As a result, a space is kept between the blade edge 1a and the inner surface of the side wall 20a. 
The reason why the biasing direction of the blade is reversed is for accommodating the cutter knife to both right handed users and left handed users. This is explained with reference to FIGS. 3A and 3B, which are partially broken end elevations seen from the user side who is grasping the cutter knife.
FIG. 3A shows a situation where a left handed user uses the cutter knife, which corresponds to the case where the slider 10 shown inside the dash-lined frame in FIG. 1 and the blade 1 connected thereto are inserted into the sleeve member 20. In FIG. 3A, the blade edge 1a faces downwards. The user grasps the cutter knife in his left hand, and manipulates the slider knob 18 attached to the slider 10 with his left thumb for protruding and retracting the blade 1. The blade 1 is connected with the slider 10 at the engagement protrusion 16, and the engagement protrusion 15 in disengagement can be seen from the user side. The slider knob 18 is in threaded engagement with a threaded hole 17 provided on the slider.
FIG. 3B shows a situation where a right handed user uses the cutter knife, which corresponds to the case where the slider 10 and the blade 1 connected thereto are inserted into the sleeve member 20 as shown by the solid-lined arrow in FIG. 1. Also in FIG. 3B, the blade edge 1a faces downwards. The user grasps the cutter knife in his right hand, and manipulates the slider knob 1a attached to the slider 10 with his right thumb for protruding and retracting the blade 1. The blade 1 is connected with the slider 10 at the engagement protrusion 15, and the engagement protrusion 16 in disengagement can be seen from the user side.
In the conventional cutter knife as explained above, with reversing the inserting direction of the slider, right handed users and left handed users can properly use it. However, the construction of the slider is inconveniently complicated. Specifically, in order to provide the spring member 11 constructed an shown in FIG. 2 on the slider 10, it is necessary to attach a separate member of a leaf spring on the slider 10, Alternatively, even if a spring portion is integrally formed into the slider 10, a very complicated mold would be necessary, which would increase the cost.
In view of the above-mentioned circumstance, an object of the present invention is to provide a cutter knife, which has simpler construction and can be properly used by both right handed users and left handed users.
According to the present invention, there is provided a cutter knife, comprising: an elongated sleeve member, a blade slidably held in the sleeve member, and a slider which is connected with the blade and is slidable in the sleeve member in the longitudinal direction, via which the blade is manipulated to protrude from and retracted into the sleeve member. The slider is provided with a first engagement protrusion and a second engagement protrusion located on the forward end and the rearward end in the sliding direction of the slider, one of which is to be inserted into a connection hole of the blade for connecting the slider and the blade. The distance from each of the first engagement protrusion and the second engagement protrusion to an inner surface of one of the sidewalls of the sleeve member when the slider is inserted into the sleeve member is smaller than the distance between the connection hole and the back of the blade. The back of the blade is thereby biased against the inner surface of the sleeve member to keep a space between the edge of the blade and the inner surface of the other sidewall of the sleeve member while the blade is sliding. The first engagement protrusion and the second engagement protrusion are aligned parallel to the sliding direction of the slider. Thus, when the inserting direction of the slider into the sleeve member is reversed, the biasing direction of the blade is also reversed,
In the cutter knife constructed as above, when the facing direction of the blade and inserting direction of the slider are reversed, the biasing direction of the blade against the inner surface of the sleeve member is reversed. This advantage itself can be achieved also in the above-mentioned conventional cutter knife. However, in the present invention, the biasing force is attributed to the location (or arrangement) of the engagement protrusions provided on the slider. Thus, any separate members (such as a spring member 11) for providing the biasing force are not necessary, and thanks to this, the construction of the slider can be more simplified than in the conventional cutter knife. Accordingly, the cutter knife can be easily manufactured, leading to a lower manufacturing cost and a lower selling price.